OTA updates

Updating over-the-air (OTA) means having the ability to push software to a device or group of devices via a network, usually without any end user interaction with the device. For this to happen, we need a central server to control the update process and a protocol for downloading the update to the update client. In a typical implementation, the client polls the update server from time to time to check if there are any updates pending. The polling interval needs to be long enough that the poll traffic does not take a significant portion of the network bandwidth, but short enough that the updates can be delivered in a timely fashion. An interval of tens of minutes to several hours is often a good compromise. The poll messages from the device contain some sort of unique identifier, such as a serial number or MAC address, and the current software version. From this, the update server can see if an update is needed. The poll messages may also contain other status information...